Most commercially available disposable absorbent products like sanitary napkins and diapers comprise synthetic superabsorbent polymers (SAP), typically polyacrylates, to deliver body fluid absorption and retention characteristics. Although such synthetic absorbent materials exhibit outstanding absorption capacity towards de-ionized water, their absorption capacity towards electrolytes/salts-containing solutions like menses is lower. It is assumed that the presence of electrolytes, proteins and cells (mainly red cells in menses) interfere with the swelling process of the absorbing gelling materials (see for ref. P. K. Chatterjee, B. S. Gupta, “Absorbent Technology” Elsevier 2002; pages 455-457).
Whereas synthetic superabsorbent polymers have been found to work very well to absorb simple fluids like urine, their performance is disappointing in feminine care applications where at least part of the fluid to be absorbed is menstrual fluid. This can lead to the failure of the feminine care product to efficiently absorb the menstrual fluid and eventually leakage and soiling of the user's garments.
US 2004/0122390A1 discloses low evaporative absorbent products. The low evaporative absorbent products comprise a treatment agent in the absorbent core of the absorbent product which, upon activation, coats swollen superabsorbent products present in the absorbent core to reduce evaporation therefrom. Several suitable treatment agents are disclosed, including cationic starch, poly(diallyldimethyl ammonium chloride), chitosan hydrochloride and trehalose.
GB 1,576,475 discloses absorbent cross-linked starch material having a degree of substitution of the cross-linking groups of 0.001 to 0.02 and which is substituted by ionic groups which are attached to the starch by ether linkages. The starch derivatives disclosed are substantially water-insoluble containing at least 90% of insoluble carbohydrate. However, it was found by the present inventors that these water-insoluble starch derivatives were not optimum for femcare applications where at least part of the fluid to be immobilized contains menses. Without wishing to be bound by theory, it is believed that the relative high amount of cross-linkers taught in GB 1,576,475 to provide insolubility may hinder the specific substances contained in menses such as proteins and red blood cells to react with the modified starch.
U.S. Pat. No. 5,780,616 discloses cationic polysaccharides having superabsorbent characteristics. The polysaccharides are substituted by quaternary ammonium groups, having a relatively high degree of substitution of at least 0.5. The polysaccharide is preferably cellulose. The polysaccharides are cross-linked to a sufficient extent that they remain insoluble in water.
WO 2006/029519A1 discloses guanidinated polysaccharides, and their use as absorbents. Although starch is mentioned as a possible polysaccharide, all the examples are chitosan based.
U.S. Pat. No. 6,887,564, to Procter & Gamble, discloses disposable absorbent products comprising chitosan material and an anionic absorbent gelling material. However, the high cost of chitosan materials has prevented until now their commercial uses.
From the above considerations there is the need for a material having a high ability to immobilize menses at an affordable price.
It has now surprisingly been found that certain cationic modified starches can deliver performance comparable to chitosan derivatives in absorbent products for feminine protection. The modified starches of the invention may be more water soluble than previously suggested. The modified starches of the invention may be synthesized by using relatively lower level of cross-linking agent than previously suggested. It was also found that a relatively lower degree of substitution for the quaternary ammonium groups than previously suggested was adequate for feminine protection applications.
Cationic modified starches can have the further advantage to come from a raw material (starch) largely available and potentially cheaper compared to chitosan salts.
The cationic modified starches of the invention perform particularly well in presence of proteinaceous fluids such as menses and deliver fluid-handling benefits, and may have better ability to increase the viscosity of blood-based fluids than other starch derivatives already described. Without wishing to be bound by theory, it is believed that the cationic modified starches of the invention have a unique combination of characteristics that make them optimized towards menses-immobilization.